From mboxrd@z Thu Jan  1 00:00:00 1970
From: Grant Likely <grant.likely-s3s/WqlpOiPyB63q8FvJNQ@public.gmane.org>
Subject: Re: [RFC] Device Tree Overlays Proposal (Was Re: capebus moving
 omap_devices to mach-omap2)
Date: Fri, 9 Nov 2012 12:06:02 +0000
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To: Tony Lindgren <tony-4v6yS6AI5VpBDgjK7y7TUQ@public.gmane.org>
Cc: Kevin Hilman <khilman-l0cyMroinI0@public.gmane.org>, Wood Scott-B07421 <B07421-KZfg59tc24xl57MIdRCFDg@public.gmane.org>, Matt Porter <mporter-l0cyMroinI0@public.gmane.org>, Tabi Timur-B04825 <B04825-KZfg59tc24xl57MIdRCFDg@public.gmane.org>, Koen Kooi <koen-QLwJDigV5abLmq1fohREcCpxlwaOVQ5f@public.gmane.org>, Pantelis Antoniou <panto-wVdstyuyKrO8r51toPun2/C9HSW9iNxf@public.gmane.org>, linux-kernel <linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>, Felipe Balbi <balbi-l0cyMroinI0@public.gmane.org>, Deepak Saxena <dsaxena-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>, Russ Dill <Russ.Dill-l0cyMroinI0@public.gmane.org>, "linux-omap-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" <linux-omap-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>, "devicetree-discuss-uLR06cmDAlY/bJ5BZ2RsiQ@public.gmane.org" <devicetree-discuss-uLR06cmDAlY/bJ5BZ2RsiQ@public.gmane.org>
List-Id: devicetree@vger.kernel.org

On Mon, Nov 5, 2012 at 11:22 PM, Tony Lindgren <tony-4v6yS6AI5VpBDgjK7y7TUQ@public.gmane.org> wrote:
> Hi,
>
> * Tabi Timur-B04825 <B04825-KZfg59tc24xl57MIdRCFDg@public.gmane.org> [121105 13:42]:
>> On Mon, Nov 5, 2012 at 2:40 PM, Grant Likely <grant.likely-s3s/WqlpOiPyB63q8FvJNQ@public.gmane.org> wrote:
>>
>> > Jane is building custom BeagleBone expansion boards called 'capes'. She
>> > can boot the system with a stock BeagleBoard device tree, but additional
>> > data is needed before a cape can be used. She could replace the FDT file
>> > used by U-Boot with one that contains the extra data, but she uses the
>> > same Linux system image regardless of the cape, and it is inconvenient
>> > to have to select a different device tree at boot time depending on the
>> > cape.
>>
>> What's wrong with having the boot loader detect the presence of the
>> Cape and update the device tree accordingly?  We do this all the time
>> in U-Boot.  Doing stuff like reading EEPROMs and testing for the
>> presence of hardware is easier in U-Boot than in Linux.
>>
>> For configurations that can be determined by the boot loader, I'm not
>> sure overlays are practical.
>
> I guess the beaglebone capes could be stackable and hotpluggable if
> handled carefully enough.

And even if it can't on the beaglebone, it will happen somewhere else.
I don't want to exclude that use-case just because nobody thought
about it.

g.